The major aims of this project include studies on the interaction of gonadotropins (human choriogonadotropin and/or lutropin) with Leydig tumor cells. The relationship(s) between degradation of the receptor-bound hormone, activation of steroidogenesis, down regulation of hormone receptors, termination of hormonal activity and target cell desensitization will be explored. Other experiments on the mechanism of action of gonadotropin include studies on the role of intra and extracellular cholesterol as a source of substrate for steroidogenesis and on the different metabolic steps that are activated by steroidogenic stimuli. Using cultures of Leydig tumor cells we will also investigate the turnover of gonadotropin receptors, and the endocrine factors that regulate Leydig cell function.